Electronic circuit designers face a seemingly relentless demand for new electronic devices that can provide increasingly sophisticated capabilities and offer ever greater bandwidth operability. This demand is reflected in the drive to integrate various digital and analog components in smaller areas, using fewer chips. Indeed, a frequently-cited goal is to create an integrated system on a single chip, a so-called “system-on-a-chip” (SoC) in which a small crystal of silicon or other semiconductor material would be fabricated to carry out each of the various electronic functions of an entire system. Aided by advances in processing technologies, electronic circuit designers are moving ever closer to this goal by increasingly integrating various digital and analog components. The result is an ever increasing array of chips that integrate varied mixed-signal circuits, including integrated RF and microwave circuits.
As chips become more complex, the need for more accurate testing of such circuits will almost certainly increase. This is largely due to the fact that in most instances the expenses associated with complex testing equipment and time lost in testing are among the more significant factors contributing to the costs of designing and manufacturing new, ever more complex integrated circuits (ICs). Accordingly, if costs are to be constrained in the face of unabated demand for more complexity and more integration, there will necessarily need to be better techniques for testing mixed-signal ICs.
A key component of an embedded test capability for an RF/Microwave IC is a high-performance test signal source. Existing techniques for providing such a test signal have typically proved to be inadequate at frequencies above the 5 to 10 gigahertz (GHz) range. At these frequencies, factors such as package parasitics make it difficult to determine the best signal levels to apply with respect to an IC under test.
Conventional approaches to providing a test signal also have involved the use of an on-chip oscillator as a simple on-chip signal generator for which only dc voltages are needed to make the oscillator work. The evolving state of technology that has lead to ever smaller, ever faster complementary metal-oxide semiconductor (CMOS) devices has exposed some shortcoming in the use of on-chip oscillators. With current technology, it is possible to design a high frequency voltage-controlled oscillator (VCO) in a standard CMOS device; for example, the design of a 50 GHz CMOS VCO has been demonstrated. The VCO-based signal generation, however, suffers from problems such as frequency drift, which can seriously degrade the quality of the generated signal.
Commercial RF/Microwave signal sources have to date typically been bench-top units. For those on-chip test signal generators implemented in the digital domain, the fastest have generally been limited to frequencies of no more than around 1 GHz. Moreover, most conventional oscillator/resonator-type sources have been found to suffer from uncertain frequency drift and phase noise performance since they typically are not controllable and accessible.
It follows, therefore, that there is a need for an effective and efficient high-performance test signal source for RF/Microwave ICs. Such a source is needed, if an effective embedded test capability for RF/Microwave ICs is to be achieved.